Many building methods involve the application of cementitious material to the face of a wall, including stucco, adhered masonry, and other similar applications. Typically, a weather resistive barrier (“WRB”) is applied over the exterior sheathing of the wall, such as plywood, and then a lath or mesh is fastened to the exterior sheathing over the WRB. The lath, which may be metal, fiberglass, or a polymer-based material, provides for mechanical keying of the unhardened stucco or plaster.
In this type of wall construction, the cementitious material itself may be relatively porous. Further, joints or discontinuities in the wall construction may provide a path for water to migrate behind the cementitious material. Condensation may also occur at different points within the wall. In sum, it is not uncommon for moisture to find its way behind the stucco or adhered masonry surface.
Accordingly, the WRB behind the stucco or adhered masonry surface provides a drainage plane against which water may accumulate and drain to the bottom of the wall. At the bottom of the wall, a weep screed or similar structure that provides the bottom edge for the cementitious material may also provide weep holes that allow the water to exit the wall. In some cases, a drainage material, such as a water channel material, may be provided between the WRB and the lath to facilitate the drainage, as generally discussed in U.S. Pat. No. 9,127,467.
In a traditional example application as described above, the wall may include thermal insulation that is located inboard of, or inside, the exterior sheathing. For instance, fiberglass insulation may be unrolled and placed in between the vertical wall studs to which the exterior sheathing is attached. In such an example, the thermal insulation is discontinuous at each of the stud locations within the wall cavity.
Increasingly, modern energy codes and building code standards have begun to call for continuous thermal insulation, which generally takes the form of a foam insulation board, such as polystyrene, that is installed outboard of, or exterior to, the exterior sheathing and over the WRB. The lath is then applied outboard of the continuous insulation. The insulating material is generally impervious to water, aside from the seams that occur between adjacent pieces of the foam insulation board. Thus, a system with dual drainage planes is created—a primary drainage plane on the exterior face of the continuous insulation and immediately behind the lath (and drainage material, if included), and a secondary drainage plane located behind the insulating material, at the WRB. In addition, current best practice is to use a drainage mesh between cladding and the continuous insulation (similar to adhered veneers using a water channel material and spacers without the lath member disclosed in U.S. Pat. No. 9,127,467).